lathers

Lather, and its plural form lathers, refers to the foam produced by soaps or detergents when they are mixed with water and agitated. The term can describe multiple foams observed during washing or, less commonly, people who lather. Lathers are central to many cleaning and grooming practices, from handwashing to shaving and laundry.

Lather forms when surfactant molecules migrate to the air–water interface, lowering surface tension and enabling bubbles to form. The foam is stabilized by a thin film surrounding each bubble, which may include additional foaming agents or polymers. Foam quality and stability depend on the type and concentration of surfactant, water temperature, pH, and the mineral content of the water (water hardness). Hard water and some minerals can reduce foam formation or alter its texture unless formulations include chelating agents or higher surfactant levels.

In practical use, lathers aid cleaning by providing lubrication, suspending dirt, and helping distribute soap over surfaces. However, the amount or richness of foam is not a reliable measure of cleaning effectiveness; products can be effective with little foam, and overly rich foam can resist rinsing if not followed by thorough rinsing.

Lathers are particularly important in shaving, where a stable lather reduces friction and delivers glide for blades, and in laundry and dishwashing, where foam helps suspend soils for removal. Modern detergents often aim for environmentally friendly foams with biodegradable surfactants and reduced or eliminated phosphates.